Increasing Polymerization Temperature Research Articles

Temperature‐Optimized Synthesis of SiO2‐Reinforced N‐(Alkyl)Acrylamide‐Based Semi‐IPN Hybrid Gels Functionalized with Methacrylic Acid Units

AbstractIn order to obtain a pH and temperature sensitive hybrids with a controlled structure, synthesis of N‐(alkyl)acrylamide‐based semi‐interpenetrating polymer network (semi‐IPN) reinforced with silica (SiO2) nanoparticles and functionalized with methacrylic acid units is carried out by optimizing the polymerization temperature. The study aims to understand the effect of polymerization temperature on the physical properties of semi‐IPN hybrids. Changing preparation temperature between −30 and 23 °C leads to significant differences in physico‐mechanical results, swelling tendency and adsorption ability, while silica nanoparticles strengthen hybrid walls, preventing their collapse during deswelling and providing rapid response. The hybrids prepared at higher temperatures are found to swell more and faster in water, while the lowest swelling is observed those prepared at 5 °C. The incorporation of SiO2 particles into copolymer structure via physical crosslinking with network chains enhances the elasticity. The effect of polymerization temperature on adsorption is investigated using methylene blue as a model dye. Increasing polymerization temperature increases the adsorption rate and shortens time to reach the equilibrium point, and adsorption efficiency increases when polymerization temperature is lowered. The results show that semi‐IPN hybrids loaded with silica nanoparticles can be used as alternative and potential adsorbents in the treatment of industrial wastes.

Synthesis of Nano-ZnO Composite Polystyrene Acrylic Emulsion and Its Application in Chinese Painting Pigments

With the continuous development of coating technology and environmental protection concepts, coating has become an indispensable item in the field of architecture and industry. Styrene acrylic emulsion as a new type of waterborne paint has attracted much attention since its emergence. Its functional modification is the focus of research, but the research results have not been ideal. To further improve the performance of styrene acrylic emulsion, nano-ZnO composite polystyrene emulsion was synthesized by emulsion polymerization, and its properties were analyzed. Aiming at the problem that nanopigments are prone to agglomeration, corresponding solutions are proposed, and the stability of nano-coatings is preliminarily studied. The inherent culture and essence of traditional culture and art is the wealth of realizing the unique nationalization and internationalization of design works. There is a lot of artistic quintessence in traditional Chinese painting art that can be used for reference to visual communication design. Through in-depth understanding and learning of Chinese painting theory and techniques, designers’ aesthetic abilities and innovation abilities can be qualitatively improved. First of all, the emulsion polymerization was carried out by semicontinuous method. The composite polystyrene emulsion containing different content of nano-ZnO was successfully prepared, which was recorded as N, Z, Z15, Z25, and Z35, respectively. The properties of the emulsion were determined, and the solid content, monomer conversion, viscosity, water absorption, and bacteriostatic effect of the emulsion were determined. The experimental results show that the solid content of emulsion Z15 (nano-ZnO content is 15%) reaches the highest value of 43.5%. The content of monomer in the emulsion affects the solid content, but the higher the monomer content, the better the solid content. The highest monomer conversion of Z15 was 86.4% at 80°C. The monomer conversion increased with the increase of polymerization temperature and tended to be stable after reaching the highest value. In the absence of nano-ZnO, the viscosity of the emulsion is the highest, and the viscosity of the emulsion decreases with the increase of the content of nano-ZnO monomer. Z35 (when the content of nano-ZnO is 35%) is the highest, which is 18.91%. The water absorption increases with the increase of nano-ZnO content. The content of nano-ZnO in the emulsion increased, the MIC value became smaller, and the bacteriostatic effect became better and better. This indicates that nano-ZnO composite polystyrene emulsion has good monomer conversion, super water resistance, and bacteriostatic effect, but its viscosity is relatively poor.

Ring-Opening Polymerization of Triaziridine Compounds in Water: An Extremely Facile Method to Synthesize a Porous Polymer through Polymerization-Induced Phase Separation.

Dissolution of trifunctional aziridine compounds, 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate] (3AZ) and tetramethylolmethane-tri-β-aziridinylpropionate (3AZOH), in water initiates a ring-opening polymerization and successful yields the corresponding network polymers via cationic polymerization. The polymerization of 3AZ induced phase separation and produced porous polymers under a wide range of monomer concentrations and polymerization temperatures. The phase separation rate in the 3AZ/water system was estimated by quantifying the turbidity by means of light transmission where transmittance decreased with an increase in the content of phase-separated materials. The rate increased with an increase in reaction temperature. The 3AZ porous polymers showed characteristic surface morphologies, which were formed by connected particles with diameters of about 4-5 μm. The porous polymers were not breakable by the compression test under 50 N. The Young's modulus of the 3AZ porous polymers increased with an increase in polymerization temperature, which may be accounted for by cross-linking through the formation of quaternary ammonium salt formed by a termination reaction. The 3AZ porous polymer absorbed various solvents.

Modulating physico-mechanical, swelling, and adsorption properties of fibrous nanoclay embedded anionically-modified semi-IPNs as new promising materials

Semi-IPN nanocomposite cryogels based on anionically modified polyacrylamide and a fibrous nanofiller sepiolite (SEP) have been designed. To achieve a homogeneous filler dispersion within semi-IPN matrix, synthesis is performed via in situ polymerization in the presence of anionic comonomer sodium acrylate (NaA). Interfacial interactions between SEP and semi-IPN matrix have been studied. Effect of incorporation of anionic NaA, linear polymer PEG and SEP on elasticity and swelling was investigated. Uniaxial compression tests were performed to measure effect of SEP content and polymerization temperature on elastic modulus. In comparison with SEP-free semi-IPNs, mechanical properties of nanocomposites have been improved with addition of SEP. In particular, for semi-IPN nanocomposite cryogels with 5.0% (w/v) of SEP, a 17.8-fold increase in compressive modulus was observed compared to semi-IPN without SEP. Real effective crosslinking density of semi-IPNs presented by a cubic polynomial as a function of SEP. While swelling decreased with an increase in SEP, it increased with an increase in polymerization temperature. Swelling of semi-IPNs was investigated in twelve different sets of solvent with different solubility parameters and chloroform/n-hexane was found as best solvent combination. Semi-IPN gels exhibited high sensitivity to pH and on-off switching behavior as reversible swelling and de-swelling was recorded at pH 2.1–11.2. Dynamic swelling was analyzed to evaluate diffusion mechanisms of water. Diffusional exponent n < 0.5 found to predict sorption mechanism of water at pH 11.2 indicated that swelling was mainly diffusion controlled. Saline sensitivity of semi-IPNs was investigated to understand effect of counterion on equilibrium swelling. Increasing salinity concentration led to a significant decline in swelling and response to counterions is reverse of classical Hofmeister series. In order of decreasing expansion ratio, anions followed order of l− ≈ NO3− > Br− > CI−. Both methylene blue and SEP caused important modifications on microstructure of semi-IPN matrix, leading to changes on adsorption and diffusional behavior. Ho’s pseudo second order model best described kinetics of adsorption process which renders nanocomposites promising for efficient removal of cationic dye, Methylene Blue.

The Effect of Polymerization Temperature on the Properties of Polyvinyl Fluoride Polymerization in Supercritical Carbon Dioxide

The ongoing search for environmentally friendlier alternative to the organic solvents used in chemical processes has led to the development of technologies based on supercritical carbon dioxide (scCO2), which is non-flammable, non-toxic and relatively inert fluid. Polymer chemistry does not escape this trend. Fluoropolymers prepared in scCO2 have many special properties, which are different from fluoropolymers that use water as the reaction medium, this paper studies the effect of polymerization temperature on polyvinyl fluoride polymerization in supercritical carbon dioxide. The results show that as the polymerization temperature increases, the intrinsic viscosity and shear viscosity of the polymer gradually decreases; at the same time, the increasing of polymerization temperature leads to higher proportion of irregular structure of the polymer, which causes lower melting point and lower crystallinity, and the film prepared by the resin also exhibits a higher visible light transmittance. The above results show that the resin polymerized in supercritical carbon dioxide can impart better performance to conventional polymerization, which expands the potential application fields of the resin.

Effect of external electron donor on stereoselective Copolymerization of isoprene and butadiene with MgCl2-Supported Ziegler-Natta catalyst

External electron donors (ED) play significant roles in regulating stereoselectivity and catalytic activity of MgCl2-supported (TiCl4/MgCl2) type Ziegler-Natta catalysts. Investigating the contribution of ED on copolymerization of isoprene (Ip) and butadiene (Bd) with TiCl4/MgCl2 Ziegler-Natta catalysts is little reported. Herein, we reported the effects of three alkoxysilanes including dimethyldimethoxysilane (DMDMS), diphenyldimethoxysilane (DPDMS), phenyltrimethoxysilane (PTMS) added as ED on trans-1,4 stereoselective copolymerization of Ip and Bd using TiCl4/MgCl2-triisobutylaluminium (Al(i-Bu)3) catalyst system. Copolymers generated by TiCl4/MgCl2 catalyst in the absence of ED featured the microstructure transformation from cis-1,4 and trans-1,4 mixed microstructure on initial stage to trans-1,4 dominated microstructure and the molecular weight (Mw) evolution from low Mw to high Mw, indicating the transformation from low trans-1,4 stereoselective active center C*-1 to high trans-1,4 stereoselective active center C*-2. Appropriate introduction of alkoxysilane donors improved the polymerization activity, trans-1,4 unit content and molecular weight of copolymer in the order of PTMS > DPDMS > DMDMS, while excess alkoxysilane donors caused the decrease in that of polymerization behaviors. Increasing polymerization temperature also promoted the enhance in catalytic activity and trans-1,4 stereoseletivity of TiCl4/MgCl2 catalyst in the presence of ED. The equilibrium between deactivation and activation effect strongly depended on alkoxysilane structure, concentration and temperature. Plausible mechanisms for stereoselective transformation of active centers in Ip and Bd copolymerization using MgCl2-supported type Ziegler-Natta catalyst were proposed in terms of special roles of ED.

Preparation and characterization of polyacrylonitrile for carbon fiber manufacture by photo-induced polymerization

The control of the molecular weight of polyacrylonitrile and its distribution is important for carbon fiber preparation. Polyacrylonitrile was synthesized by photo-induced solution polymerization using acrylonitrile as the monomer and dimethyl sulfoxide as a solvent. The molecular weight and molecular weight distribution of the polyacrylonitrile were respectively determined by a viscosity method with an Ubbelohde viscometer and gel permeation chromatography. The functional groups on and the chain structure of polyacrylonitrile were analyzed by infrared spectroscopy and nuclear magnetic resonance spectroscopy. Results showed that with an increase of polymerization temperature or monomer concentration, the conversion of the monomer and the molecular weight increased. Compared with the traditional initiator-induced radical polymerization of acrylonitrile, photo-induced polymerization significantly narrows the molecular weight distribution. Polyacrylonitrile with both a high molecular weight and a relatively narrow molecular weight distribution was manufactured by photo-induced solution polymerization.

Synthesis and characterization of polystyrene/poly(ethyl acrylate) mushroom‐like Janus particles

AbstractFavorable though isotropic polymeric structures are in many applications, they are not optimized in some others. Janus particles, having two sides with completely different properties, are optimizing the use for these applications, from industrial emulsifiers to biomedicine. In this work, mushroom‐like Janus particles made of PS as the seed and PEA as the semispherical centers through (seeded) dispersion polymerization were synthesized. Afterward, the effects of the initiator, monomer, and stabilizer amount as well as polymerization temperature were studied. It is shown that, in the PS synthesis stage, an increase in polymerization temperature, initiator amount, and monomer amount, as well as a decrease in stabilizer amount, lead to an increase in particles' size and in PDI percentage. In addition, in the next stage, the synthesis of mushroom‐like particles with the PEA sites, an increase in initiator amount, monomer amount, and polymerization temperature, as well as a decrease in stabilizer amount lead to bigger PEA centers and in excessive amount. It is also shown that above the breakthrough, three‐part particles increase in number with the changes mentioned. It is concluded that with the determined optimized conditions in this work mushroom‐like Janus particles of PS/PEA can be synthesized.

Inclusion of isolated α-amino acids along the polylactide chain through organocatalytic ring-opening copolymerization

Degradable polymers based on α-hydroxy acids and α-amino acids constitutes a potent class of biomaterials, combining high hydrolyzability with structural features that mimics peptides. Driven by the design criteria to construct isolated α-amino acid units along a main polylactide chain, a copolymer system was developed based on two monomers with distinctly different equilibrium behaviors. This was uncovered by detailed understanding on the kinetic and thermodynamic polymerizability of 3S,6S-dimethylmorpholine-2,5-dione (DMMD) and L-lactide (LLA) at low reaction temperatures. Under Brønsted base-promoted ring-opening copolymerization (ROCOP) conditions, the equilibrium nature of the copolymerization was shown susceptible to changes in the system, such as catalyst basicity, solvent polarity and initial monomer concentrations. Subsequently, high equilibrium conversions of both monomers with control over molecular weight and dispersity could be achieved within short reaction times by modulation of these factors. Thermodynamic elucidations of the copolymerization system revealed that DMMD behaved as an unstrained monomer with a large propagation barrier, favored by an increase in polymerization temperature. Ultimately, the high propagation barrier of DMMD in the system resulted in a kinetically controlled mechanism with the formation of completely isolated units of DMMD along the polylactide backbone. These results extend current ROCOP strategies of morpholine-2,5-diones and cyclic esters to a mild and selective copolymerization platform for the construction of sequence-controlled α-amino acid decorated polyesters for medical applications.

Propylene Polymerization Catalyzed by Metallocene /Methylaluminoxane Systems on Rice Husk Ash.

Silica generated from agricultural waste is more cost effective and environmentally friendly than silica from traditional commercial processes. In this study, spherical silica particles with a diameter of around 120 nm were fabricated from rice husk ash (RHA), and were used to support two bridged zirconcene complexes ((I) Me2Si(Ind)2ZrCl2 and (II) C2H4(Ind)2ZrCl2) for catalyzing propylene polymerization to produce polypropylene (PP) in a temperature range of 40–70 °C and in a solution methylaluminoxane (MAO) range of 0.1–0.6 wt%. Due to its small particle size, RHA-supported catalyst exhibited much higher activity than micro-sized commercial silica-supported catalyst. At the optimum polymerization temperature of 55 °C and with increasing MAO concentration, polymer yield increased proportionally with the increase of number average molecular weight. Compared to (I), (II) produced more polymer molecules but with much shorter chain length, ascribed to the differences of Zr loading and bridge structure. With increasing polymerization temperature, polymer molecular weight decreased rapidly and resulted in a significant change of PP assembly morphology (shape and size). At 55 °C, (I) produced uniform PP assemblies which had dumbbell-like structure with a smooth middle section and two fibrillar ends, while (II) produced spherical PP particles. The dumbbell middle part width was essentially identical to the Batchelor microscale proposed in turbulent mixing theory.

An assessment of dynamics of electrochemical polymerization of pyrrole

In this work, the dynamics of electrochemical polymerization of pyrrole was assessed by measuring the system current and polymer yield under different cell dimensions and polymerization conditions. The effects of distance between electrodes on the yield and system current were described. Also, the effects of monomer concentration and electrode size on monomer-to-polymer conversion were critically analyzed with respect to the energy supplied to the system. The enthalpy of the process was also determined. It was observed that the yield was directly proportional to the product of system current and time when sufficient monomer and electrode space for deposition of polymer were available otherwise the electrical energy was transformed more into heat energy. Electrochemical polymerization of pyrrole was found to be an exothermic process, and the enthalpy of polymerization increased with an increase in polymerization temperature.

Synthesis of aliphatic polycarbonates by irreversible polycondensation catalyzed by dilithium tetra-tert-butylzincate

Diethyl carbonate was reacted with phenol or 1,6-hexanediol with 5 mol% dilithium tetra-tert-butylzincate (TBZL) as a catalyst at 25 or 70 °C. The exchange reaction with phenol did not occur under these conditions, while that with 1,6-hexanediol did. Thus, polycondensation of diphenyl carbonate with 1,6-hexanediol was investigated. As expected, poly (hexamethylene carbonate) was obtained without removal of the by-product phenol. Conversion reached over 99% with increasing polymerization temperature. Additionally, 1,5-pentandiol and 1,9-nonanediol were also suitable diols for the polycondensation. Aliphatic polycarbonates with number-average molecular weights of 10,000 or more were obtained under optimum polymerization conditions. Polycondensation catalyzed by TBZL proceeded faster than that by titanium tetraisopropoxide, which is used as a general catalyst for polycondensation of diesters, dialkylcarbonates, and diphenyl carbonate with diols. Polycondensations with TBZL proceeded under atmospheric pressure in the presence of the by-product phenol. This polymerization system is expected to be applicable to various diols.

Synthesis and Characterization of Novel Azido Polymers: Hyperbranched Poly-3-azidomethyl-3-hydroxymethyl Oxetane

In the past thirty years, azido polymers have attracted wide attention in the field of energetic materials. Currently, the synthesized azido polymers have linear structure. In the present research, hyperbranched poly-3-azidomethyl-3-hydroxymethyl oxetane (HBPAMHMO) was synthesized using an AB2 monomer, and its physical and chemical properties were studied. The results showed that the molecular weight of HBPAMHMO increased along with the increasing ratio of r ([monomer]0/[initiator]0), together with very narrow PDI (from 1.12 to 1.34), and moreover, the degree of branching increased along with the increase in polymerization temperature. As compared to linear azido polymer with similar structure, it has lower glass transition temperature, sensitivity, higher combustion heat and mechanical properties, suggesting a great prospect for numerous applications.

Microstructural study of synthesized polyethylenes by homogeneous and heterogeneous nickel α-diimine catalysts

In this work, ethylene polymerization was investigated by using homogeneous and heterogenouse nickel α-diimine catalysts [1,4-bis(2,6-diisopropylphenyl) acenaphthene diimine nickel(II) dibromide]. Methyl aluminoxane (MAO) and triethyl aluminum (TEA) were used as cocatalysts in homogenous and heterogeneous polymerizations, respectively. The heterogeneous catalyst showed lower activity than its homogeneous equivalent. The influence of polymerization temperature and heterogenization conditions was studied on the microstructure properties of the prepared polymers. Increasing polymerization temperature (T P) up to 50 °C decreased the activity of both homogenous (LN) and heterogeneous (LNS) nickel α-diimine catalysts. The highest activities were 1286 and 982 kg PE (mol Ni bar h)−1 obtained at T P = 30 °C for LN and LNS catalysts, respectively. The polymer samples obtained by supported catalyst (LNS) showed lower unsaturation contents. Moreover, DSC analysis did not show any melting peaks for polymers obtained by LN catalyst due to their amorphous structure, which was confirmed by XRD analysis. The microstructure of the prepared polymers was completed by successive self-nucleation annealing (SSA) and was investigated by 13C NMR studies. The SSA thermogram of samples made by LNS catalyst exhibited several crystal types with different lamella thicknesses. The branches in polyethylene samples produced by homogenous catalyst were higher and showed more diversity. The total methyl branch percentages for both LN and LNS catalysts were 13.1 and 3.4%, respectively.

아미노-기능화된 실리카 위 후전이 금속 촉매 담지 및 이를 이용한 노보넨 중합

In this study, an amorphous silica was functionalized with aminosilane, N-((3-trimethoxysilyl)propyl)ethylenediamine (2NS) and the late transition metal catalysts including ((DME)NiBr2 and PdCl2(COD)) were subsequently immobilized on the func- tionalized amorphous silica for norbornene polymerization. Effects of the polymerization temperature, polymerization time, Al/Ni molar ratio, and type of co-catalyst on norbornene polymerization were investigated. Unsupported late transition metal catalysts did not show any activities for norbornene polymerization. However, the SiO2/2NS/Ni catayst with MAO system, with increasing polymerization temperature, increased the polymerization activity and decreased the molecular weight of the polynorbornene (PNB). Furthermore, the catalyst when increasing polymerization temperature caused the decrease in both the polymerization activity and molecular weight of PNB. This confirmed that the stability of SiO2/2NS/Ni at a high temperature was greater than that of SiO2/2NS/Pd. Also the longer polymerization time resulted in the higher conversion of norbornene for both catalysts. When the Al : Ni molar ratio was 1000 : 1, the highest activity (15.3 kg-PNB/ (µmol-Ni*hr)) but lowest molecular weight (Mn = 124,000 g/mol) of PNB were achieved. Also SiO2/2NS/Ni catalyst with borate/TEAL resulted in di- minishing the polymerization activity and molecular weight of PNB with increasing the polymerization temperature.

L-Lactide Ring-Opening Polymerization with Tris(acetylacetonate)Titanium(IV) for Renewable Material.

A new Ti-type of catalyst for L-lactide polymerization was synthesized by reaction of titanium(IV) isopropoxide (TTIP) with acetylacetone (AA). Moreover, PLA was prepared by the bulk ring-opening polymerization using synthesized Ti catalyst. Polymerization behaviors were examined depending on monomer/catalyst molar ratio, polymerization temperature and time. The structure of synthesized catalysts was verified with FT-IR and 1H NMR and the properties of poly(L-lactide) (PLLA) were examined by GPC, DSC and FT-IR. There existed about 30 minutes of induction time at the monomer/catalyst molar ratio of 300. The molecular weight (MW) increased as monomer/catalyst molar ratio increased. The MW increased almost linearly as polymerization progressed. Increasing polymerization temperature increased the molecular weight of PLLA as well as monomer/catalyst molar ratio. The melting point (T(m)) of polymers was in the range of 142 to 167 degrees C. Lower T(m) was expected to be resulted from relatively lower molecular weight.

DSC Kinetics Analysis for the Synthesis of Three‐Arms Poly(ε‐caprolactone) Using Aluminum Tri‐sec‐Butoxide as Initiator

ABSTRACTThe kinetics of the ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) initiated by soluble aluminum tri‐sec‐butoxide (Al(OsecBu)3) has been investigated by the differential scanning calorimetry (DSC). The DSC polymerizations were carried out under nonisothermal and isothermal conditions to obtain three‐arms poly(ε‐caprolactone) (PCL). From nonisothermal DSC, the polymerization rate (dα/dt) increased with increasing heating rates. The values of Ea were determined from Kissinger ( kJ mol−1), Friedman (31.0 – 63.0 kJ mol−1), and Starink (64.0 – 71.0 kJ mol−1) methods. From isothermal DSC, the dα/dt and the apparent rate constant (kapp) increased with increasing polymerization temperatures. The ROP of ε‐CL initiated by Al(OsecBu)3 occurred via the coordination insertion mechanism. The number average molecular weight () and percent yield of the synthesized PCL was enhanced by increasing polymerization temperature. The synthesized PCL with of 2.4 × 104 was obtained using a molar ratio of monomer to Al‐O active center ([M]/[Al‐O]) of 400 at 150ºC for 24 h. Al(OsecBu)3 is one of the promising initiator due to its solubility, low transesterification reaction, and high efficiency in ε‐CL polymerization.

Synthesis of surfactant-free hydroxypropylcellulose nanogel and its dual-responsive properties

Surfactant-free hydroxypropylcellulose (HPC) nanogels were synthesized by using thermo-sensitive HPC as a template to form HPC/PMAA nanoscale complex. The formation mechanism was owing to the interpolymer hydrogen bonding between HPC and PMAA induced phase transition of HPC in aqueous media. The average size of the resulting HPC nanogels ranges from about 98 to 241nm. It was found that the average size of HPC nanogels changed little with increasing polymerization temperature below 26°C, whereas it greatly increased above 26°C. When the concentration of HPC was increased from 0.1 to 0.9wt.%, the diameter of nanogels decreased firstly and then increased. Besides, an increasing crosslinker BIS concentration led to a reduced size of HPC nanogels, and the nanogels had the narrowest size distribution when its concentration was 0.1wt.%. In addition to intrinsic thermo-sensitivity, HPC nanogels also display pH-induced phase transition due to pH-responsive PMAA contained in HPC nanogels. Surfactant-free, dual-responsive HPC nanogels would have promising applications in biotechnology and nanomedicine.

Kinetic evidences for reversible transformations of active centers in ethylene polymerization by titanium–magnesium catalyst: Effect of the polymerization temperature

The kinetics of ethylene polymerization at varied polymerization temperature over two modifications of titanium–magnesium catalysts that differ in their compositions and the molecular weight of the resulting polymers were studied by polymerization quenching by radioactive carbon monoxide. An increase in polymerization temperature in the range of 40–80 °C was found to significantly increase the number of active centers (CP), which contributes to the polymerization rate more significantly than an increase in the propagation rate constant (kP) does. The rise in the number of active centers with increasing polymerization temperature is shown to result in effective activation energy (Eeff) determined from the temperature dependence of polymerization rate being significantly higher than the activation energy of propagation reaction (EP) determined from the temperature dependence of the kP value. It was shown too the changes of the number of active centers and polymerization rate at variation of temperature in the single experiment have the reversible nature. The data on the number of active centers and the propagation rate constants at ethylene polymerization in the presence of hydrogen as a chain transfer agent are obtained. Introduction of hydrogen reduces the number of active centers at elevated polymerization temperatures (60–80 °C) and has virtually no effect on the CP value at lower temperatures; it also reduces the kP value at 40–80 °C. The findings on the effect of polymerization temperature on the number of active centers were used to propose a kinetic scheme including the reaction of reversible transformation of the precursors of active centers (alkyl derivatives of titanium) into an inactive state due to adsorption of a co-catalyst (triethylaluminum). The transformation of these complexes into active centers depends on polymerization temperature, presence of hydrogen, concentrations of monomer and organoaluminum activator.

Direct synthesis of highly reactive polyisobutylenes via cationic polymerization of isobutylene co‐initiated with TiCl4 in nonpolar hydrocarbon media

ABSTRACTLiving cationic polymerization of isobutylene (IB) with 1‐chlorine‐2,4,4‐trimethyl pentane (TMPCl)/TiCl4/isopropanol (iPrOH) or isoamylol (iAmOH) has been achieved in the presence of 2,6‐di‐tert‐butylpyridine (DtBP) at −80°C. Polyisobutylenes with nearly theoretical Mn based on TMPCl molecules and more than 90% of tert‐chlorine‐end groups could be obtained at high [TMPCl]. The β‐proton elimination from CH3 in growing chain ends increased with increasing polymerization temperature and decreasing solvent polarity. A chain‐transfer‐dominated cationic polymerization process with H2O/TiCl4/iAmOH could be achieved in n‐hexane at −30°C. The monomer conversion and content of exo‐olefin end groups increased while molecular weight decreased with increasing [iAmOH]. To the best of our knowledge, this is the first example to achieve the direct synthesis of highly reactive polyisobutylene with low Mn of 1200∼1600, carrying more than 80% of exo‐olefin terminals by a single‐step process via cationic polymerization co‐initiated by TiCl4 in nonpolar hydrocarbon. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42232.